VANADIUM STEELS 189 Further, there are some types of tungsten steel, especially the chrome- tungsten steels, which, although they have not a high content of tungsten are difficult to dissolve in nitric acid. In such cases, when the action of the nitric acid ceases, a few drops of cone, hydrochloric acid are added this being repeated until the attack of the metal is complete. The tungstic acid freed from silica may often contain small amounts of iron and chromium. In this event, the weighed residue is fused with sodium-potassium carbonate, the mass treated with hot water and the insoluble residue, consisting of ferric oxide, filtered off, washed, ignited and weighed. The chromium is determined volumetricaUy in the filtrate (see p. 183). 2. Determination of the Carbon.—For products readily attacked by acids, the Corleis method may be used, whilst, for the others, direct combustion in a current of oxygen must be employed (see Iron, i)'. 3. Determination of the Manganese, Phosphorus and Sulphur.- The determination of these elements may be effected by the methods de- scribed under Iron, 3, 4 and 5. For some determinations, such as that of the phosphorus, use may be made of the hydrochloric acid solution from which the silica and tungstic acid have been removed. * * * Tungsten steels usually contain 2-10% of tungsten (but sometimes 20% or more), 0-5-1-5% of carbon, 0-2-0-7% °^ silicon, 0-4-2-5% of manganese and, in some cases, small quantities of phosphorus ; a good tungsten steel should not, however, contain more than 0-015% of phosphorus. Cast-and wrought-iron, and ordinary steels do not usually contain tungsten. VANADIUM STEELS Owing to their hardness and their resistance to shock and vibration, vanadium steels are used for the framework of locomotives, automobile parts, tools, etc. Their analysis includes estimations of the elements normally present in steels (carbon, silicon, manganese, phosphorus, sulphur, etc.) as well as that of vanadium and, sometimes, of nickel, chromium and molybdenum, which very often accompany vanadium in special steels. 1 . Determination of the Vanadium. — If the vanadium is transformed, by fusion with an oxidising agent, into vanadic acid, it may be determined, according to Holverscheit, iodometrically ; the vanadic acid is reduced by means of hydrobromic acid, the bromine liberated in the reaction 1 being collected in potassium iodide solution and the iodine thus set free titrated with thiosulphate. Procedure. 2-3 grams of the sample are dissolved in nitric acid (D i-i8) in a small porcelain dish, the liquid evaporated to dryness, the residue ignited and the oxides obtained fused in a nickel crucible with 12-18 grams of sodium peroxide, as described for chrome steels. The mass obtained is lixiviated with hot water and the residue insoluble in water dried and aHBr = H2O + Br2. of nickel for the determination.